1. Field of the Invention
The primary field of the invention relates to devices for illumination of limited areas to assist security personnel in performing assigned tasks in hidden or covert situations. Specifically, the flashlight provides enough light in areas of close proximity for the user to perform necessary tasks such as map reading, walking or equipment operation or maintenance while minimizing the possibility of the user being located by hostile observers with their unaided vision or with image intensifiers. In some situations the flashlight may be used as a specialized signaling device.
2. Related Art
Security officers and others are frequently required to conduct surveillance tracking and other operations within eyesight of persons they wish to observe. The task has always been dangerous because, if hostile persons, such as criminals, see the using officer, they may attack him. Presently, it is even more risky because the criminals have access to image intensifiers capable of magnifying very small amounts of light and displaying it on a screen. A variety of these intensifiers are available. Thus previously used covert lighting devices are now unacceptable because they can reveal the officer's location even when the lighting device is set to very low intensities. Other occurrences and features of traditional lighting devices which can reveal the officer's location include the time it takes to adjust the lighting intensity level, the decay time of energy radiation after the power is disconnected, accidental dropping of the lighting device when in the switched-on state and specular reflections of light from nearby surfaces.
A portable lighting device, disclosed in U.S. Pat. No. 4,517,628, granted to applicant, provided means for changing the color of the illumination from incandescent white light to filtered red light for use in blackout conditions; however, that concept is now inadequate as a covert signal light because the radiant energy decay time span is excessive. This device is vulnerable to detection even after it is off because the incandescent filament continues to emit reddish light until substantial cooling has taken place.
U.S. Pat. No. 4,677,533, issued to applicant, et al, discloses a lighting device intended for color discrimination having a combination of colored electronic lamps alone or in combination with an incandescent lamp and with separate electrically variable controls for the adjustment of brilliance of the illumination spectra. With this device specular reflections from illuminated objects or the careless and accidental misaiming of the light may subject the user to a higher probability of detection by hostile observers than is now acceptable for covert operations.
The rheostats taught in U.S. Pat. No. 4,677,533 produce a continuous and slow change in color which is inferior for signaling applications. The rheostat/switch designs are also faulted in an effective covert light which must ideally turn "OFF" instantaneously. This cannot be achieved if the power is turned "OFF" by an intensity control device such as a rheostat which slowly decreases the current and intensity before the actual "OFF" position is reached. The unfiltered incandescent lamp used in some embodiments prevents instantaneous darkening of the device even when the power is instantaneously turned off. Finally, the coordinated rheostat/switch prevents the device from instantaneously being switched from "OFF" to usable lighting intensity.
Other improvements in lighting devices are disclosed in U.S. Pat. Nos. 4,947,291 and 4,963,798, both issued to applicant. Among the featured improvements of the disclosures are components and circuits for the reduction of radiant energy in the infrared wavelengths, for the synthesis of specific radiation spectral patterns, and for dimming the radiated light and for monitoring battery power.